1. Field of the Invention
The present invention relates to a benzimidazole derivative having a rust preventing effect and to a composition for the treatment of surfaces of copper and copper alloys comprising the benzimidazole derivative which is particularly useful in preventing rust in printed-wiring boards.
2. Description of the Background Art
Methods for prevention of rust in a circuit formed from copper or a copper alloy on a printed-wiring board and for maintaining the adherence of solder include a method of covering the circuit with another metal, for example, a method of plating with solder, gold, palladium, or the like, a method of coating with solder by the so-called hot air leveler method, and a method of covering with an organic film.
Examples of materials which form the organic film used in the last-mentioned method include a rosin-type preflux, which coats the entire printed-wiring board, and an alkylimidazole-type preflux which forms a film by a chemical reaction selectively on the copper circuit section.
The rosin-type preflux is used in a method for forming a film by coating, spraying, or soaking the entire printed-wiring board with a solution of a natural rosin, a rosin ester, a rosin-modified maleic acid resin, or the like, in an organic solvent, and then drying. However, this method involves a problem of impairing the working environment and the safety because of volatilization of the organic solvent.
The alkylimidazole-type preflux is soluble in water and is superior from the aspect of keeping a good working environment and safety. The compound, however, deteriorates when subjected to a high temperature, hindering the action of a postflux which is used during soldering and thus giving a rise to the drawback of poor solder adherence.
In recent years, a surface mounting method has become the most commonly used method for joining electronic parts on a printed-wiring board. This increases opportunities wherein printed-wiring boards are exposed to high temperatures, e.g., temporary mounting of the parts, reflow of creamy solders, and the like. For this reason, a treatment agent which does not lower the adherence of the solder, even when the printed-wiring boards have been exposed to high temperatures, is required.
An invention responding to such a requirement is disclosed in Japanese Patent Laid-open (ko-kai) No. 124395/1991, which provides a preflux using a benzimidazole derivative with a hydrogen atom, an alkyl group, or an aryl group in 2-position of the imidazole ring.
Although the benzimidazole derivatives can satisfy the above-mentioned heat resistance requirement to a certain degree, they cannot be a breakthrough for the ever increasing requirements more stringently imposed on the adherence of the solder after exposure to a high temperature.
In view of this situation, the present inventors have synthesized a number of compounds and studied their applicability as a preflux and their heat resistance. As a result, the present inventors have found that certain novel benzimidazole derivatives can produce superior films on the surfaces of copper or copper alloys, which can be excellently soldered without using a volatile solvent even after the surfaces have been exposed to a high temperature.